Method and apparatus foe measuring



Jul 15, 1941. R. w. ATKINSON METHOD AND APPARATUS FOR MEASURING ECCENTRICITY IN TUBULAR CONDUCTORS Original Filed llarh 10, 1934 3 Sheets-Sheet 1 32 unluunn'o INVENTOR 31191 n. flr/rwsay July 15, 1941.

v R. w. A'l'KlNsoN Original Filed March 10', 1934 3 Sheets-Sheet 2 A R we A Nb a A 2:5 a mw I H V a a a H! L. M g Q m HHH HIVHIIHIHI ATTORNEYS July 15, 1941.

R. w. ATKINSON METHOD AND APPARATUS FOR MEASURING ECCENTRICITY IN TUBULAR CONDUCTORS 3 Sheets-Sheet 3 Original Filed March 10. 1934 INVENTOR AuP/I Win/#50 I line-H.

Reiaued Jul 15, 1941 Original No.

715,030, March 10,1934.

ma'rnon m mana'ms roa MEASURING ccaN'rRIcl'r! nv rumnna connuc'rons K ntian w. Atkinson, Westileld, n. 1.,

General ,Cable Corporation. New York, N. corporation of New Jersey 2,200,827, dated May 14, 1940,

assignor to Y a Application for reissue Ma! 10, 1941, Serial No. 392,988

36 Claims. (Cl- 175-483) This invention relates to a method and ap' paratus for measuring variation in the thickness of tubular electrical conductors. More particularly, the invention is concerned with measuring and recording the eccentricity of a tubular conductor such .as the metal sheath enclosing one n'more insulated conductors. It is an object o the invention to provide'an improyed method and apparatus\for measuring and recording varlation in .aiewmem ss of-tubular conductors.

Other objects and advantages of the invention will appeal-hereinafter.

The invention will be best uncherstood from the -following description when read in the light'of the accompanying drawings illustrating certain specific embodiments ofthe invention.

- In the drawings:

Figure l is a diagrammatic representation of one embodiment of the invention;

Figure 2 illustrates a modified electrical circu'it:

. Fig. 3 illustrates a further modification of the electrical circuit; s

Figure 4 is a side elevation of one suitable apparatus through which the conductorpassesin )paking the measurement;

Figure 5 is an elevation looking at the righthand end of the apparatus shown in Figure 4;

and

Figure 6 is a vertical section through the apparatus shown in Figure 4, substantially on the In metal sheathed cables the sheath usually is in the form of a continuous lead tube extruded about. the insulated conductor or conductors. Desirably, the sheath thickness is-uniiorm both circumferentially and longitudinally of the cable. Due to the variations in temperature the volume of the insulating compound with which the cable is filled changes from time to time. On account of the incompressible nature of the compound, the eilect' of the sheath in restraining the expansion with increased temperature is negligible, and consequently the sheath must expand to acc'o modate the increase in volume. i

If the sheath wall is of uniform thickness circumferentially, this expansion is accomplished by a small, approximately uniform percentage of stretch around the complete circumference.

however, the sheath is eccentric, the greater part of the stretch will occur at the thinnest part of the circumference and the percentage stretch of this portion will be much more than when the elongation is distributed in the case of a uniform sheath. Where conditions are such that oil flows longitudinally along the cable after the cable has cooled,-refllling the expanded sheath, a new expansion and stretching will occur in the case or a new heating. Then withsuccessive expansions, this eil'ect will tend to be cumulative and may ultimately result in rupture of the thin section. with a concentric sheath, the total stretch being distributed uniformly around the circumi'erence results in greatly reducing the maximum amount of stretch in any one section and the danger of sheath failure from this cause.

Furthermore, if the thickness of the, cable sheath can be accurately controlled andkept uniform within narrow limits it may be possible in some cases to use somewhat thinner sheaths with the same degree of safety now attained.

Not only is it important to know whether or not a cable sheath-is eccentric, but the actual amount of eccentricity".should be accurately known, and desirably thelocation of the eccentricity longitudinally of the cable should be known. The importance of these measurements will be apparent when it is realized that 'even though the extruding die be accurately adjusted at the beginning of the sheathing operation to give a concentric sheath, this adjustment may vary as the sheathing operation proceeds. Heretoiore, no means have been available to-continmeasure the thickness of the cable sheath I uously as the sheath is applied. Desirably any variation in the thickness of the sheath wall circumferentially of the sheath is measured as the cable comes from the extruding machine. If this measurement provides a continuous indication or record of any eccentricity in the cable sheath it is a relatively simple matter to makethe necessary adjustment of the extruding die in well known manner to restore the sheath to uniform circumferential thickness. For this purpose it is desirable not merely to know when the eccentricity of the sheath exceeds a certain predetermined amount, but it is important to havea continuous measurement of the actual amount of eccentricity.

According to thepresentinvention a method and apparatus are provided for continuously recording variation in the thickness of a tubular conductor circumferentially of the conductor, whereby eccentricity not only is indicated, but the actual variation in thickness of the sheath wall is continuously recorded. While the inven tion is described with particular reference to the measurement of cable sheaths, it will be obvious l ngth by the flux within the sheath vever, remain the same so that the generated itheslip turn Figure 1 illustrates; diagrammatically one'particular apparatus for measuring the thickness of a tubular conductor and for making a permanent record of any variation in the thickness of the conductor. Means are pl'ovidedfor establishing aflow of current circumferentiaily in the tubular conductor II, and conveniently this means corn-v prises a coil I! through which the conductor moves eo-axially. The coil II is connected..as by means of the leads It, to a source oi' alternatlng current.- Flow of current through the coil It sets up a magnetic field surrounding the eoiiwhich induces a current flow circumferentiallyin the tubular conductor ll. 7

'l'wol contacts ll andil, desirably mounted within the coil I! substantially midway of its length. engage the conductor II at circumferene tially spaced points lying in a plane perpendicular to the longitudinal axis of the conductor. In the illustrative embodiment of li'igure 1 the contacts II and II are spaced apart at an angle of 90 degrees. 4

If the sheath is uniform in thickness circum ferentially and centrally located in the coil J2, the voltage drop in any portion of-a circumferential path in the. sheath due to the current flowing in the'sheath will be'exactlyequal tn the voltage generated in that portion of the path bytheiiu'xsetupbythecm'rentin coil ll and no potential diil'erence will exist between contacts lland ll. Ifthethicknessofanyportion o! the path is diilerent from the average thickerably twisted together, instrument; If it is desired to merely have a nose for the whole circumference, the resistance drop inthispartper unit lengthwillbecorrethat of the average for spondingly-diii'erent from circumference. The voltage set up per unit will, howvoltage and the resistance drop will no longerequal, and a difference in potential will now appear. This diii'erence in potential is proportional to thedeviation of the sheath thickness between the contacts from the average thickness.

If the conductor is rotated relative to the concurrent galvanometer' or uring device may be connected to the contacts .Where a singlepairoi' contacts aroused it is necessary to move the contacts relative to the conductor in a circumferential as well as longituginal direction inorder to obtain a measuremen of nally of the cable. the rotation of the contacts maybe relatively slow. i

irom the contacts H and II, respectively; are the electrical leads II and i1, preferably twisted together, which connect with the rings is and Is. The slip rings lland is about the conductor I4 and II. netic field Theleads lland'lllieinthemagthe soil It, and conseuuently a voltage will be induced directly in these leads in 4 conductor between the contacts and additiontotheresistancedmpinthe I with the contacts done ansss I than the reslstance drop in the tubular conductor. Conveniently, such means introduces into the circuit a voltage degrees out of phase with the induced voltage. As shown in Figure 1,

a compensating coil II located adjacent to the tubular conductor and within the magnetic field tmsurrounding it, is voltage other than that existing in the tubular conductor between the contacts II and II.

it connected by means of the conductors, prefto a suitable measuring connected in the head i1, and

visual indication of variation in conductor thickness, the leads I! may be connected directly to conductor as it moves tacts II and il will 7 vanometer reading which is proportional to the variation in in the conductor. Therefore. it is possible to calibrate the galvanometer scale to directly the actual variation in sheath thickness.

Where voltage in the tubular conductor between the contacts is and II is referred to. this means the root mean square value of the alternating voltage having the same frequency as that of the exciting coil II. in the root mean square voltage during a revolution of the brushes around the tubular conductor, values during a cycle of the which gives a measure ductor thickness;

Ordinarily. it will be desirable manent record of variation in pressed voltage to make aperthe thickness of a cable sheath. andconveniently this may be I! a graphic milby connecting to the leads livolllneter. The term graphic millivoltrneter is used herein to denote broadly any means for balanced relation. thereupon means are a m l y to vary the point .ofmntact on the slide'wire and restore the voltage balance. This last mentioned voltage. co spondingtothepointatwhichcontactismadeonthe siidewire. and since thisvariationwillbe prothickness of the hibularconductoatherecordsomadeisanaccurate representations! the conductor eccentrieity.

Ref

connected to one resistance 28. The other lead 22 is connected thjoigh "a variablelesistance I4 and a galvanorneter to a contact 2| "Ind The endsof'theslidewire is the slide wiremovable therealong in the manner here-- coil may be adjusted to compensate for the the slip rings is and "are brushes It is the-variation and not the change in instantaneous of variation in the 0on brought into operation" erringa'gaintol'igureLoneoftheleads endllofthesiidewire a1,sss

are connected, as by means of theleads II to a source of alternating current. Desirably, one of the leads I8 includes'a variable resistance 2! are adjusted sothattheresistancedropmthe slide wire ll between .the end It to which one o! the leads I! is connected and the contact II.

is 180 degrees out 01' phase with the resistance drop in the tubular conductor between the contacts I4 and I5, and so that the voltage drop over the whole slide wire is such as to give the desired voltage sensitivity ofthe instrument.- The sensitivity adjustment is such that all desired measurements are on the instrument scale andyc large enough for accurate feading.

Desirably the coil I! which induces a circumterential current flow in the tubular conductor- II, and the slide wire resistance II are connected to the same source 01 alternating current ll, for example through separate windings on a common transformer, or by means of separate transformers. By deriving the induced and aphasechangingcireuit I. which initially set up by the coil II it is evident that unless it is possible to establish a symmetrical condition with respect to the-effect oi the field on the leads-l0 and II, there will be set up potentials in these leads which may be very large in relation to the potentials which we,wish to measure. An idea of the magnitude of suchextraneous voltages may be gained by considering Figure l.

I! the leads II and I1 could be carried in from v the contacts radially to the 'center oithe conductor and carried from there twisted together,

voltage in the tubular conductor and the balancing voltage in the slide wire from the same source, any variation in the voltage of the alternating current source willibe ineiiectlve to destroy the balanced relation. If these voltages were derived from diii'erentsources, any variation inthe voltage of either source might produce an indication oi eccentricity in the tubular conductor when actually there was no such eccentricity,- or might produce an inaccurate indication oieccentricity;

Where a record is made of variation in the thickness of the tubular conductor, as illustrated in Figure l, the galvanometer 2! serves as a control instrument for causing operation of the voltage balancing means automatically .in respouse to variation in the circumferential resistance of the tubular conductor between the contacts I and IS.' If this resistance in the tubular conductor varies as the eonductor'moves under the contacts, the needle of the galvanometer is moved from its zero position an amount proportional to the, change in resistance.

At regular intervals, for example every second, a device not shown in Figure 1 is operated. and if the galvanometer needle has moved from its conductor in oppini zero reading, means are automatically set into I operation to move the contact I! along the slide wire resistance 23 a distance proportional to the reading of the galvanometer needle to restore the voltage balance and return the galvanometer needle to zero. The actual mechanism for moving the contact II in response to movement of the galvanometerneedle is not illustrated in the drawings for the reason that this present invention. and tor the further reason that instruments of this type are known in the art. One such instrument is the Leeds l r'Norththat it the circumferential resistance o- 'the completelycompensate for the lack of symm mechanism itseli does not form a part of the tubular conductor varies; this variation causes a voltage unbalance in the external circuit. This voltage unbalance operates automaticallyo increase or decrease the balancing yo'ltage so as to Y restore the balance.-

t record of varia- Conveniently the pe rmarie tion in the circumferentialresistance of the tubular conductor I l may 13g made by attaching to the movable contactgfih recording device such as the pen 33. under thexpen 33 is a chart- 34, upon which mo ment of the pen II and the such symmetrical arrangement would be established.

This is manifestly an-impracticable greatly reducing the sensitivity oi the instrument in order to keep the reading on the scale.

In Figures 1. 2 and'3, three methods of takin care of this eifect'are illustrated. In Figure 1, the contacts are degrees apartand the coil 20 is introduced into the circuit and this coil may be, adjusted'to compensate for the voltage induced in the leads. In Figure 2, the contacts are also 90 degrees ap' and the" leads are brought out in suchaway to provide for adiustment to approximate symmetry by means'of apotentiometer connection [8 between two leads from contact 2 are carried-around the directions. In Figure 3, the contacts are ldfii egrees apartand symmetry is obtained by ,bi'ingingtwo leads at opposite sides-oi the cable from one contact to a point adjacent the other of each pair. I Any lack/oi perfect symmetry or .failure;

will result in some shifting of the galvanom ter zero. ,If a single pair of contacts engage Jthe.

cond uctor, and these contacts ,are not rotate ad pt the conductor, it m dimcult, 11 no i m possible, t6 determine the "rrect zero onthe galvanometer."-;However, i tubul conductor is rotated relatively to thefiiontac khe zero is obtained very easily as the;me a n\ ding oi the; galvanometer, assuming that the toltages generated in the external circuit remain constant in value' and phase relation. A similar resultcan be obtained by the use of several pairs 0! non-rotating contacts symmetrically.

disposed about the tubular conductor. v

The sensitivity of the galvanometer llmay be adjusted to the most desirable condition tor diflerent sized conductors or i'or the conductors of diilerent thicknesses or resistances and the damping maintained constant by simultaneously adjusting resistance ,2! in series with the gaiarrange ment, and it will be seen that if the lead iromi ranged to maintain the correct relative setting.

Means may be provided vanometer field to maximum sensitivity, and as tlnuous record is made t nue to increase. a If the chart I trading press, 'tion of the chart to locate definitely the longivide means for shown in Figure 1 the galvanometer field coil II is connected to a source of alternating current by means 01' the leads I which include a suitable variab.le resistance 31 and phase changing circuit I With the means illustrated in Figure 1, a conof the actual amount of. variation in thickness of a tubular conductor.-

- I! this record is made for a cable sheath as the cable comes from the extruding machine, the operator can know definitely at all times whether or not the cable sheath is eccentric, and

' it the sheath is eccentric the actual amount 01' eccentricity. If the variation in sheath thickness exceeds a permissible limit at any time it is acomparatively simple matter for the operator tostop the extruding, machine and make the necessary adjustment in the die position, or means might beprovided to make this adjustment automatically in response to variation be-, y nd permissible limits. I I

It has been found that even though the die,

opening for extruding a metal sheath on an electric cable be accurately adjusted at the begin ning oi the extruding operation, the sheath may gradually becomeeccentric as the extruding operation continues. This eccentricity may conor in time may correct itself. moves under the recording pen 33 only while the cable passes through the exthen it is possible by an examinatudinal position .on the cable oi any eccentric portion shown on the chart.

, It the chant fl moves at a uniform rate oi' speed without regard to movement or cable through the extruding press, it may be desirable to promaking a separate record on the same chart or the operation of the press.- For truding press to actuate recording mechanism to show on the chart the such records While ordinarily itis not important to record whether the thin portion or an eccentric sheath is on the top, bottom or one side 01' the cable as the cable emerges from the press, a record of this conditionmay be made conveniently on the same chart 3. lbr example, a pen or other recording device might be actuated. byan electric contactor adjusted to operate when the rotating contacts J! nods I Referring to Figure 2. there is illustrated a slightly diilerent electrical circuit from that of Figured for connecting the contacts ll and" and Il are directly over the cable 'to the measuring instrument. In this embodimenta single pair oi contacts are spaced, for example at an angle of 90 degrees, around the tubular conductor, and in operation willbe rotated about the conductor. The contact ii is connectcdby means of a lead I! to slip ring 44. The contact I! is connected by means of two leads 48 and. to the slip rings" and ll re-. spectively. Itwill be noted thaihthe leads II and to adjust the galmovement of the press member. Withside by side it is possible to locate any eccentricity longitudinally of the cable.

example, means may be connected with the ex- I mylinder or ram, whichever moves,

extend in opposite directions around the tubto a point adjacent the conthe leads 0, II and ll are ular conductor |l tact u; and that twisted together from this theslipringllisabrushconnectedbythelead I! to one terminal of a suitable indicating or recording instrument II. This instrument ll might be simply a galvanometer or it might be a graphic millivoltmeter, for example of the type illustrated in Figure l. Brushes en aging the slip rings ll and I! are connected by means oi the'leads Ii and I2 to opposite ends of the resistance I3. Movable alongthe resistance It is a contact I which is connected to the other terminal or the measuring instrument ll.

With the arrangement illustrated Figure 2, any voltage induced by the coil I! in the circuit connections other than the resistance drop in the circumferential Portion of thetubuiar conductor between the contacts I and ll may be approximately balanced out in the circuit without the necessity of introducing a compensating coillllasinl igureli p Inthe discussionofl'igureslandaithas been indicated that with a concentric tube there is zero voltage between the contacts II and II or the contacts II and 42. While this viewpoint is fundamentally correct, an alternate explanationmay be used to deiine the conditions.

, Referring to Figure 1, ii the leads I. and i! are taken to the measuring instrument, in the absence of coil ll, there will be found a voltage between the terminals of these leads even with From the standpoint oi this tween contactsfiil and ll'on-a concentric'tube. that is, it is made equal and opposite to that voltage. The difference lies wholly in the expression or viewpoint: the physical performance is the same, namely the adjustment of compensation to give zero voltage at the measuring instrument in the case or a uniform concentric deflection on the tube. For a non-uniform tube.

P oportional to the dc!- instrumentwill theh be mature from uniformi I This second explanation may. now be applied to Figure 2. In this case the function oi compensa'tion supplied by coil ll of Figure 1 is supplied by the singleturn'coil I, "I! which surrounds the tubular conductor ll. Here the voltage which wouldbe obtained by the use of leads I! and II alone or II and alone is compensated by the use, of the complete turn or coil which comprises the leads II and 4' and "with the aid or 'the potentiometer It With this means the voltage between the terminals II and II is adjusted to bezero-i'or a uniform tube.

Unless precautions. are taken either to mount the slip rings shown in Figures 1 and lot a considerable distance or t shield the rings from the magnetic iield surrounding the coil voltages will be induced by the magnetic field directly in the slip rings. Or-V dina'rily, it will be desirable to mount the slippoint on. I

this voltage' betwcen theneutralize or compensate for the voltage b-' from the exciting coil II,

sliprings are made and located relative to-the coilas hereinafter described so that voltages inducedintheslipfln bythecoilaresubstantially without difect on the'opemtion of the measuring instrument. v

Desirably, the slip rings are relatively small in cross section and are made of a conducting material having a relativelyhigh electrical re- .a cross section approximately equal to that o! a. #10 conductor, and a resistance 01 about flity times that of copper. I

The slip rings desirably are located so that the surface bounded by the loci oi the centers of gravity of sections through adjacent rings is substantially parallel to the magnetic iiux surrounding the coil. It will be apparent that the relative positions oi! the slip rings will depend upon their location with respect to the mag-. netic field surrounding the coil. Ii the slip rings are mounted adjacent one end of the inducing coil this surface will lie in a plane perpendicular to the longitudinal axis of the coil.

Alternatively, one of the rings may. be so: shaped and positioned, as shown in the upper v righthand portion of Figure '4, as partly tosurround another ringin such amanner that the centers of gravity of sections through the rings are substantially coincident. The armngements describedpermit the location oi the slip rings adjacent the in'ducingcoil without resorting to magnetic shielding.

The difllculties involved-in the use of slip, rings and brushes which arerequired where the contacts are rotated aboutthe conductor, ean be eliminated by using a plurality'ot pairs of contacts arranged so .that relative rotation between necessary 1 Such an arrangement is illustrated in Figure 3,

contacts 55 -58 and 51--58, the contacts of each pair being spaced 180 degrees circumi'erentially tacts of each pair desirably have the same relation to each 'other and to the connecting leads.

A-lead 59 connects thecontact i to one terminal oi the measuring instrument, and a lead site directions about the tubular conductor H to 'a point adjacent the contact 53 connects the contact 5G to the other terminal oi the measuring instrument. Similar leads 8 1 and I connect with the. contacts 51 and It.

I With"'two'pairs of contacts as illustrated in Figure 3, two separate measuring instrummts "Emig'ht be employed, one a each pair of contacts.

6' for connecting the instrument iirst'to one pair 01'. contacts and then to the other pair oi contacts.

More'than two pairs may be used to obtain given by rotating'contacts. In this case the simpie two'pole double-throw switch in Figure 3 may conveniently be replaced by a multiple point rotary switch'., This arrangement hasthe very material advantage oi. oislip rings andr'otating parts in that part of the device through which-the cable passes as it comes irom thepress.

Figures 4, 5 and of non-rotating contacts aboutthe tubular conductor ll. .Where a pluralityoi pairs 01' con cts are employed. the con-v Gil having branches iii and 82 extending in oppoinstrument connected to- However, satisfactory resuits can be obtained by employing a singlemeasuring instrument '8! and a suitable switch- QLBBS sistance. For example, each slip ring might have I secured Desirably the base. member Ii and the stand-' ards Hand 1: are made r insulating material. RotatabIy supported between the standards is a horizontal coil unit for inducing circumferenti'al iiow 01' current in the tubular conductor- II, for example a cable sheath, as the cable passes through the coil. Desirably the coil imit is axially aligned with the isheathed cable. as the cable emerges from the lead press, not shown. In Figure 4, the cable or other tubular conductor ii moves from left to right. I

Mounted in the standard 12 adjacent its upper corners and extrgiding' inwardly are thespindles 15, upon each which is rotatably mounted a dies 11 and I8. Rotat'ably mountedon the spindle I1 is a gear I! and a bearing ilii. Mounted on the spindle ll is a similar gear and a similar hearing. The gear on the spindle Ills rigidly to the spindle, and the spindle =is. connected, for example, through a worm. gear speed reducer I! with an electric motor ll. Desirably the bearings, and gears 'rnpunted on the spindles 15, TI and II are'made of insulating material;

the tubularc'onductor and the contacts is unthere being in this embodiment two pairs of and the gear 31 are made of insulating material.

Movement of the coil unit longitudinally be-' a mounted on spindles 89 secured in the standards standard I! so that it may be replaced with other guides for diflerentsiaed conductors. As shown more nearly the results:

eliminating the necessity The c011 unit is supported with its cylindrical end rings l5 and 86 restingon the bearings on the spindles l5, l1 and 18, whereby the coil unit may be readily rotated about its longitudinal axis. Secured on the end ring I6 is a. gear 81 which engages the gears mounted on the spindles l1 and II, whereby the coil unit may be rotated through the driving connection with the motor ll. Desirably the end rings 85 and II tween the standards" and i3 is prevented, for

example, by. means oi the bearings 88 rotatably I,.and the bearing ll rotatably mounted on the spindle ll secured in the upper end of the standard II. In prior art devices it was customa y nd considered essential to .rotate the contacts once ior'every inch of length of the cablesheath; in one satisfactory operating embodiment of the present invention the contacts made one rotation for every 'ten' feet of length of the cable sheath. This is about 1% of the rotational .speed formerly required. y

The upper end of the standard 13 desirably is provided with a guide. I2 which aids in centering the conductor in the coil unit as the conductor moves longitudinally through the coil. Conveniently the guide 82 is easily removable from the in Figure 4, additional guiding means such as the-sheave ll may be employed for directing the path of the conductor after it leaves .the guide It.

Theend-ringsll and li oi the coil unit are rigidly securedtoeachotherinspaced relation,

as-by means ot'three metal struts 14', which form with the end-rings a cage. In the illustrative embodiment, the coil for inducing dlcllmfetential currentilowinthe tubular conductor is dividedinto two sections "and M. Eachsectlon of 6 illustrate one'suitable apps 7s coil is wound on a tube, one end rains for inducing circumferential new of curof which projects beyond the end ,0: the coil winding and is secured in the central opening through the adJacent end ring. The two sections of the coil may be connected electrically in series or in parallel, and the coil are connected to the slip rings 01 mounted, for example, on the outer face of the end ring ll. .Current is supplied to the cell through the slip rings I1 and brushes 98 mounted in the standard". Y L

As may be seerfmore clearly in Figure 6, intermediate the coil sections 05 and II is a plate ll, secured along its edge to the struts ll. Desirably this plate 89 is made of insulating material. The plate has a central opening ill of substantially the same diameter as the inside diameter oi the cylindrical tubes upon which the coil is wound.

The plate serves as a mounting for the contacts eng gingcthe tubular conductor, and conveniently serves also as a support for means for centering the conductor axially within the coil Mounted in the plate, and extending from both faces thereof, are four pivot pins ill. Pivotally mounted on these pins III, are the rockers III, I, I and llll. Similar rockers are mounted on both faces of the plate I, and corresponding rockers on opposite sides of the plate are rigidly secured to turn together as by means of spacing blocks lli secured to the rockers with screws. i I a The outer ends of the rockers are connected by means of links I", IN and I" so that the rockers all turn about their several "pivots together. The inner ends of the rockers define an.

opening through which the tubular conductor Ii passes, and the size 01' this opening may be ad-,

justed readily for different sized conductors.

Conveniently. this adjustment is controlled by a mean of a screw III which may pass through openings in the rockers I02 and through an arcuate slot ill in the upper end of the plate II. Desirably, means are provided such as the spring I. tending to turn the molten; so as to maintain the inner ends'of the rockers in guiding engagement with the conductor. g I

Conveniently the contacts H and II which engage the tubular conductor are mounted in the forked ends of a flat member 0! insulating material III, which in turn may slide in a radial slotl II in the plate 9!. Conveniently, means are provided to move the contact carrying member i it in the slot" I automatically-as the conductor guiding rockers turn about their pivots.

In Figure 6, the outer end of the member III has secured therein a pin Ill projecting from both faces of the member through a slot III in a plate Bland engaging the upper surfaces-of the rockers m. Secured in the upper edge 'of the rocker III are screws III carrying a spring pressed plate i II which serves to keep the pin III in engagement with the upper edge of the rocker I02. It will be apparent that as-the rocker I02 is turned about its pivot III, the contact bearing member III will be moved radially toward and away from the conductor i I. The compensating coil 20 which is shown in Figure 1 is not shown in Figure 6, but conveniently this coil, comprising only a turn or two of wire, mounted within the member Ill. v

The slip rings by which connections are made to the contacts ll and llv desirably are locatedon the outer face of the gear II, as shown in Figures 4 and 5. In the illustrative embodiment therearetwoofthese sliprings land ligand would bedesirably they are mounted directly over the end of the coil winding,as'showninl 'igure 4.

.Theslipring lllisshapedsoastopartiysurround the slip ring 8 in such a manner thatthe centers of gravity of sections through the rings are substantially coincident. The advantages of this arrangement have been set forth in the preceding description. The slip ring- H8 is generally a shallow U-shape. Connection from the contact engaging the tubular conductor to the slip ring Ill convenientlyv will be made through an opening in the bottom of the U- shape. Substantially the same result may be accomplished if the slip. ring Ill is made in the form of two separate rings, one on either side of the ring Ill, having jumper connections at intervals circumferentially of the rings.

, Conveniently, the brushes engaging the rings 8 and II! are mounted in thestandard 13. Desirably these brushes are small in cross section, are located near together, and are mounted on the same radius of the coil all to reduce the voltage induced by the coil.

Applicant has provided'an improved method and an improvedapparatus for measuring accurately variation in the thickness of a tubular conductor, and for making a record of any-variation in thickness.

It will be understood that the present invention maybe variously modified and embodied within the scope of the subjoined claims.

Iclaim:

1. Apparatus for measuring variation in the I points spaced circumferentially about the contwo contacts for engaging the conductor at points spaced circumierentially about the conductor,

ductor, an external circuit including" means for balancing the voltage between the spaced contacts on the conductor surface with a voltage 180 degrees out of phase, means for causing relative movement between the conductor and the spaced contacts, and means operating automatically'in-response to any voltage unbalance in the external circuit caused by variation in the resistance of the conductor between the contacts 'as the contacts move over the conductor suriace to adjust the voltage balancing means and restore the voltage balance in the external circuit.

.2. Apparatus for measuring variation in the thickness of a tubular conductor comprising, in combination, means for causing an electric current to flow circumfe'rentially in the conductor,

an external circuit includingmeans for balancin the voltage between the spaced contacts on the conductor surface with a voltage 180 degrees out of phase, means for causing relative movement between the conductor and the spaced contacts, means operating automatically in response to any voltage unbalance in the external circuit caused by variation in the resistance of the conductor between the contacts as the contaicts move over the conductor surface to adjust the voltage balancing means and restore the voltage balance in the external circuit, and means for recording continuously any variation in the con-.

ductor thickness as evidenced by the adjustment of the voltage balancing means.

3. Apparatus for measuring variation in the thickness of a tubular conductor comprising. in combinatiommeansforcausinganelectriccurord. of the amount of variati external circuit rent to flow circumierentially in the conductor, contacts ior'engaging the' conductor at points spaced circumier'entially about the conductor, an external circuit for balancing the voltage between the spaced contacts on the conductor surface with a voltage 180 degrees out of phase, means for causing relative movement between the conductor andithe spaced contacts, and means for measuring continuously any voltage unbalance in the external circuit. caused by variation in the a resistance of the conductor between the contacts 'as the contacts move over the conductor surface.

4. Apparatus according to the preceding claim wherein the current flowing in the tubular conductorand the balancing voltage in the external circuit are derived from the samesource, whereby variations in the voltage of the source are ineffectual to destroy the voltage balance in the externalv circuit. p i 5. An eccentricity detector tor tubular conductors comprising, in combination, means for inducing an electricjcurrent flow circumierentially in the conductor, two contacts for engaging the conductor at circum'ierentially spaced points, means for causing relative movement of the contacts longitudinally of the conductor, means for causing relatively slow relative rotation between the conductor and the contacts, a graphic millivoltmeter, and means connecting the contacts and the millivoltmeter to make a continuous rec o! the conductor between tie contacts as the contacts move over the. conductor surface, said last mentioned meansv including means compensating for voltages other than the resistance drop in the conductor between the contacts.

in the resistance 6. Apparatus for measuring variation in the thickness of a tubular conductor comprising, in combination, a coil through which the conductor passes for inducing an electric current flow circumferentially in the conductor, contacts for engaging the conductor at clrcumferentially spaced points substantially midway of the coil ends, means for rotating the contacts about the conductor, a graphic millivoltmeter, and means conmeeting the contacts and the millivoltmeter, said last mentioned means including means for neutralizing any voltage induced directly therein by the coil.

7. Apparatus for measiiring variation in the thickness of a tubular conductor comprising, in combination, ,a coil through which the conductor cumierentiaily of the conductor, and meansincluded in the connections between the contacts and the external circuit compensating for voltage other than the resistance drop in the sheath.

' 9. Apparatus for measuring variation in the thickness of a tubular conductor comprising, in

combination, means for establishing an electric current flow circumierentially in the conductor, a pair of contacts for engaging the conductor at circumierentialiy spaced points, means for causing relative longitudinal movement and much slower relative circumferential movement between the conductor and the contacts, a milli-- voltmeter, and electrical connections, between the contacts and the millivoltmeter, and means in additionto said connections for maintaining substantial electrical symmetry in said connections to compensate for voltage other than the resistance drop in the sheath.

' 10. Apparatus for measuringvariation in the thickness of a tubular conductor comprising, in combination, means for establishing an electric current flow circumierentially in the 'conductor, a pair of contactsfor engagingthe conductor at circumierentially spaced points, means for causing relative movement between the conductor and the contacts, a millivoltmeter, and,

electrical conn'e'ctionsbetween the contacts and the millivoltmeter, the connection from one of the.contacts including a compensating coil to make this ,connection substantially electrically symmetrical with the connection from the other contact.

11. Apparatus for measuring variation in the thickness of a tubular conductor comprising, in combination, a coil through which the conductor passes for inducing an electric current flow circumierentially in the conductor, contacts for engaging the conductor at circumferentially spaced points, means for rotating the contacts about the conductor, a graphic millivoltmeter,

and means connecting the contacts and milli-' voltmeter, including a plurality oi slip rings and brushes, said slip rings being so located that the surface bounded by the loci of the centers'oi gravity of sections through adjacent rings is substantially parallel to the magnetic ilux around the coil.

passes for inducing an electric current flow circumierentially in the conductor, contacts for engaging 'the conductor at circumferentially 'spacedpoints, means for causing relative movement longitudinally"ot the conductor between the conductor on the one hand and the coil and the contacts on the other hand; and means for causing much slower relative movement, circumierentially oi the conductor between the conductor on the one handand the coil and the,

contacts on theother hand, means connected to said contacts for measuring continuously the amount of variation in the circumferential resistance oi the conductor between the contacts,

and means iorcompensating for voltages other 12. Apparatus for measuring variationin the thickness of a tubular conductor comprising, in

combination, acoil through which the conductor passes for inducing an electric current flow circumferentially' in the conductor, contacts for engaging the conductor at circumierentially spaced points, means for rotating the contacts about the conductor, agraphic millivoltmeter.

and means connecting the contacts and the millivoltmeter including a plurality oi slip rings and brushes, said slip rings being positioned adjacent one end of the coil with the loci of the centers of gravity 01 sections through the rings in a com mon plane perpendicular to the longitudinal axis 'oithecoil.

than the resistance drop in the conductorhe tween the. contacts. 8. Apparatus for measuring variation in the thickness or a tubular conductor comprising, in combinatioma coil for inducing now of electric current circumferentially in the conductor, conconductor and. c with 'tacta en aging the for measuring the voltage ctr- 13. Apparatus for measuring variation in the thickness of atubular conductor comprising, in combination, a coil through which the conductor for inducing an electric current flow' circumferent'ially in the conductor, contacts for engaging the conductor at 'clrcumferentially spaced points, means for, rotating the contacts about the conductor, a graphic millivoltmeter, and means connecting the-contacts of the millivoltmeter, in-' cluding-a ,plurality'oi slip rings and brushes, said clip rings being made of a high resistance coneas g combination, means for stantiaily to zero when thickness of a magnetic field surrounding the coil.

14. Apparatus for in the conductor, contacts for enconductor at circumi tially spaced points. means for rotating the contacts about the conductor, a graphic millivoltmeter, means connecting the contacts and the millivoltmeter including a plurality of slip rings and brushes, said slip rings being positioned in the magnetic field iurrounding' the coil, one of said rings being so shapedandpositionedaspartlytosurround anotherrin'ginsuchamannerthatthecenters i gravity oi. sections through the rings are substantially coincident.

15. Apparatus for measuring variation in the thickness 01 a tubular conductor comprising, in

combination, means for establishing an electric current flow clrcumierentially in the conductor, of contacts for engaging the conductor at circumi'erentially spaced points, the contacts of each pair having the-same relation to each other and to the connecting leads as the contacts 01' every other pair, means torcausing relative longitudinal movement between the conductor and the contacts, and means connected to said contacts for measuring circumferential va'ri-' ation in the resistance or the conductor along its length.

l6. pparatus for measuring variation in the of a tub conductor comprising, in establishing an electric current flow circumierentially in the conductor,

variation in the resistance of the conductor along its length.

17. Apparatus for measuring variation. in the ment between the conductor andtheicontacts, a millivoltmeter, and ections between the: contacts' and the millivoltmeter which balance the potential inipressed on the millivoltmeter subthe circumferential resistance oi the conductor is uniform.

18. Apparatus for measuring variation in the tubular conductor comprising, in combination, means for establishing anelectric current flow pair oi. contacts for engaging the conductor at points spaced circumferentially oi theconductor, means for causing relative movement between the conductor and the contacts, a millivoltmeter, a lead from one of thegcontacts extending outwardly from the conductor substantially in a radial direction, two leads from the other contact extending around the conductor in opposite directions to a point adjacent the first contact and then outwardly from the conductor with the first lead, voltmeter,

19. The method oi. determining variation in the thicknessoi' a tubular conductor causing a current to flow circumferentially in the conductor, a Y

which comprises circumierentially in the of contacts. for measuring with a voltage 180 degrees out conductor. balancing the voltage between two circumterentially spaced points of phase, andcontinuously measuring any unbalance between the last mentioned voltage and the mltagebetween similarly spaced points elsewhere on the conductor.

20. The method of determining variation in the thickness of a tubular conductor which comprises causing a current to fiow circumierentially inthe conductor, balancing the voltage between two circumterentially spaced points on the conductor with a-voltage 180 degrees out of phase, and automatically restoring this voltage balance in response to any unbalance resulting from variation in the conductor resistance as the spaced points are moved over the conductor surface riation in the conductor resistance as the spaced points are moved over the conductor surface, and continuously recording any variation in the conductor thickness as evidenced by variation in 22. pp atus for measuring variation in the thickness of a tubular conductor comprising, in combination, means for establishing an electric current flow circumierentiallyin the conductor, a plurality of pairs of contacts mounted forslight movement relative to said first named means. i'or engaging the conductor at diametrically opposed'circumierentially spaced points,

means for causing relative longitudinal movement between the conductor and the contacts,

and means consecutively connected to said pairs V circumferential variation in the resistance of the conductor along its? lgngth- 23. Apparatus for measuring variation in the thickness oi atubular conductor comprising, in combination, means for establishing an electric current flow circumferentially in the conductor, a plurality of pairs or contacts for engaging the conductor at circumierentially spaced points, the contacts 0! each pair having the same relation to each other and to the-connecting leads as the contacts of every other pain-means i'or causing relative longitudinal movement between the conductor and the contacts, and means'consecutiveiy connected to said pairs of contacts for sistance oi the conductor measuring circumferential variation in the realong its length.

24. The method oi measuring eccentricity in a tubular conductor which comprises causing a current to flow circumierentially in the conductor, and continuously recording variation in the voltage between a plurality of pairs of circumi'erentially spaced contact points at a definite angular separation on the conductor surface while maintaining the. same relation; between the contacts of each pair to each other and to their connecting leads as to the contacts of every other pair and'causing the conductor to move solely in a longitudinal direction'relative to said contacts. Y 25. An eccentricity indicator for tubing composed of electrically conducting material. said indicator comprising in combination an erciting on the conductor spaced points on the con-.

' age thickness.

coil adapted to surround tubing to be tested, a compensating coil adapted to surround the tubing, a pair of contacts adapted to touch points on a circumference of the tubing, said compensating coil being arranged to constitute part of the connecting lead from one of said contacts, and current responsive apparatus operatively connected in series relation with said contacts and said compensating coil, the connections being such that voltage induced in said compensating coil acts in opposition to voltage induced circumferentially in the tubing.

26. An eccentricity indicator for tubing composed of electrically conducting m'aterial, said indicator comprising in combination, an exciting coil adapted to surround the tubing to be tested, a pair of contacts adapted to touch points on-the circumference of thetubing, a compensating coil disposed in the field of the'exciting coil adapted to adjust the-voltage measured between contacts, and current responsive apparatus operatively connected in series relation with said contacts and' said compensating coil.

27. An eccentricity indicator posed of electrically conducting material, said indicator comprising in combination an exciting coil adapted to surround tubing to be tested, a compensating coil adapted to surround the tubing, a pair of contacts adapted to touch points on a circumference of the tubing, and current responsive apparatus operatively connected in series relation with said contacts and said compensatv plurality of pairs or contactsadapted to touch for tubing commg coil, the connections being such that voltage induced in said compensating coil acts in opposition to voltage induced circumferentially in the tubing. i

28. An eccentricity indicator for tubing composed of electrically conducting material, saidindicator comprising in combination an exciting coil adapted to be connected to a source of a1- temating current and adapted to surround tubing to be tested, a compensating coil also adapted to surround the tubing, a pair of contacts adapted to touch points on a circumference of thetubing, said compensating coil being arranged to constitute part of the connecting lead from one of said contacts, and directionally responsive alternating current-responsive apparatus operatively connected in series relation with said contacts and said compensating coil, the connections being such that voltage induced in said comindicator comprising in combination an exciting coil adapted to be connected to a source of alternating current and adapted to surroundtubing to be tested, a compensating coil also adapted to surroundLthe tubing, a pair of contacts adapted to touch points on a circumference of the tubing, and directionally responsive alternating currentresponsive apparatus operatively connected in serie relation with said contacts and said compensating coil, the connections being such that voltage induced in said compensating coil acts in opposition to voltage induced circumterentially in the tubing, and the electrical dimensions being such that the. opposing-voltages are balanced in case the contacts are against a portion of the tubing of average thickness.

31. An eccentricity indicator for tubing composed of electrically conducting material, said ,indicator comprising in combination, an exciting coil adapted to surround tubing to be tested, a

points on the circumference of the tubing, a compensating coil for each pair of contacts adapted to adjust the voltage measured between contacts, said compensating coil being adapted to surround the tubing and to constitute part of the connecting lead from one of the contacts of a pair, current responsive apparatus, and means for operatively connecting said current responsive apparatus in series relation with said compensating coils and different ones of said pairs of contacts successively.

32. An eccentricityindicator for tubing composed of electrically conducting material, said indicator comprising in combination, an exciting coil adapted to surround tubing to be tested, 'a

plurality of pairs of contacts adapted to touch pensating coil acts in opposition to voltage in-.

duced circumferentially in the tubing, and the electrical dimensions being such that .the opposing voltages are balanced in case the contacts are against a portion of the tubing of aver- 29. An eccentricitylindi'cator for tubing composed oi' electrically conducting material, said indicator comprising in combination,.an exciting coil adapted to be connected to a source oi: alternating current and adapted to surround tubing .to be tested, a pair of contacts adapted to'touch points on the circumference of the tubing, a compensating coil disposed inthe field of the exciting coil adapted'to adjust the voltage measured between contacts, and directionally responsivealternating current-responsive apparatus opertacts and'said compensating coil, the electrical dimensions being such that the opposing voltages are balanced in case the contacts are against a portion of the tubing of average thickness.

30. An eccentricity indicator for tubing com posed of electrically conducting material, said points on the circumference of the tubing, a compensating coil disposed in the field of the exciting coil adapted to adjust the voltage measured between contacts, current responsive apparatus, and means for operatively connecting said currentresponsive apparatus'in series relation with different ones, of said pairs of contactssuccessively,

33. An eccentricity indicator for tubing composed of electrically conducting material, said indicator comprising in combination an exciting coil adapted to surround tubing to be tested, a

compensating coil also adapted to surround the tubing, a plurality of pairs of contacts adapted to touch points on the circumference of the tubing, current-responsive apparatus, and means for operativel'y'connecting said current-responsive apparatus in series relation with said compensating .coiland different ones of said pairs of l contacts successively, the connections being such that voltage induced in said compensating coil opposes that induced circumferentially inthe tubing. t

34. The method of measuring the eccentricity in a tubular conductor which comprises causing a circumferential flowoi current in the conductor from a surrounding exciting coil, and making electrical connection to said sheath by a pair of circurnferentially spaced contacts, con- -'necting these contacts to a voltage measuring atively connected in series relation with said condevice, and. compensating for the voltage due to the loop connection between the contacts for average conductor thickness or concentricity by placing a compensating coil in series with one of said contacts and in the field of said exciting coil.

35. The method of measuring the eccentricity in a tubular conductor which comprises causing a circumferential flow of current in the conductor from a surrounding exciting coil, and making electrical connection to said sheath by a pair of circumierentially spaced contacts, connecting these contacts to a voltage measuring device, and compensating for the voltage due to the loop connection between the contacts for average conductor thickness or concentricity by placing a compensating coil in series with one of said contacts and in the fleld 01 said exciting coil, said compensating coil surrounding said conductor.

, 36. The method 0! measuring the eccentricity in a tubular conductor which comprises causing I. circmnferential .ilow of current in the conductor from a surrounding exciting coil, and making electrical connection to said sheath by a pair of circumferenti'ally spaced contacts, connecting these contacts to.a vvoltage measuring device, and compensating fonthe voltage due to the loop connection between the contacts for average conductor thickness or concentricity by placing a compensating coil in series with one of said contacts and in the field-of said exciting coil, said compensating coil surrounding said conductor and being connected to said contact intermediate its ends.

- RALPH W. ATKINSON. 

